The present invention relates to an optical modulator module with an optical modulator therein, and more particularly to an optical modulator module for use in transmitters for optical fiber communications.
Improvements have been made to the internal configuration of electroabsorption modulator integrated laser diode modules (EA modulator integrated LD modules) having an electroabsorption modulator integrated laser diode packaged therein in order to improve their frequency characteristics. FIG. 1 is a plan view of the chip carrier portion of the electroabsorption modulator integrated laser diode module shown in FIG. 1(b) of Japanese Patent Laid-Open No. 2001-257412.
Referring to FIG. 1, an electroabsorption modulator integrated laser diode 3 and a chip capacitor 4 are mounted on a chip carrier 10. The electroabsorption modulator integrated laser diode 3 is a semiconductor device in which a laser diode 2 and an electroabsorption modulator 1 are integrated. The electroabsorption modulator 1 is optically coupled to an optical system (not shown) for optical output. The laser diode 2 receives electric power through wires 14 and 15 connected to the chip capacitor 4. A strip conductor 5 is disposed on the chip carrier 10. One end of the strip conductor 5 is connected to a signal source 11 as an input end, while the other end is electrically connected to the electroabsorption modulator 1 through a wire 12. Further, an impedance matching resistor 7 is inserted in the middle portion of the strip conductor 5. The strip conductor 5, the chip carrier 10, and a grounding conductor 6 form a high frequency line. A terminating resistor 8 formed of a thin-film resistor is disposed on the termination side of the chip carrier 10. One terminal of the terminating resistor 8 is electrically connected to the electroabsorption modulator 1 through a wire 13, while the other terminal is connected to the ground metal on the back side of the chip carrier 10 through a via 9.
FIG. 2 shows an equivalent circuit of the chip carrier portion shown in FIG. 1. The signal source 11 is connected through a transmission line (not shown) to one end of a microstrip line 23 made up of the strip conductor 5 and the chip carrier 10. The microstrip line 23 also includes the resistance R7 of the impedance matching resistor 7. The inductance L12 of the wire 12 is connected to the other end of the microstrip line 23. Two branch lines are connected to the other end on the left side of the inductance L12. One includes the electroabsorption modulator 1 indicated by a diode in the figure, while the other branch includes the inductance L13 of the wire 13 and the resistance R8 of the terminating resistor 8 that are connected in series. These branch lines are each grounded at the other end.
Thus, the electroabsorption modulator integrated laser diode module described above is configured such that the wires 12 and 13 connect between the strip conductor 5 and the electroabsorption modulator 1 and between the electroabsorption modulator 1 and the terminating resistor 8, respectively, thereby improving the waveform of the optical output or eye pattern at a transmission rate of 10 Gbps (gigabits per second).
It should be noted that Japanese Patent Laid-Open No. 2003-279907 discloses an optical modulator exciting circuit comprising a modulator, a first strip line, and a second strip line, wherein: the first strip line outputs a modulation signal to the modulator through a first resistor; and the second strip line is connected to the first strip line through the modulator and formed of a second resistor and a third resistor connected in series.
Incidentally, the more types of electroabsorption modulators there are, the more widely their capacitances vary and hence the more widely the frequency characteristics of electroabsorption modulator integrated laser diode modules using these electroabsorption modulators vary. This may leads to an increase in the return loss and/or the transmission loss of an electroabsorption modulator integrated laser diode module.
In such a case, it is necessary to redesign the chip carrier portion so as to optimize the frequency characteristics of the electroabsorption modulator integrated laser diode module. However, this requires development time and expense, thus increasing the total cost.